I have an HK. I haven't used it much yet. I would just nail together some jig for backing up narrow stock or resting the FSK guide on. You're not likely to be up on a ladder cutting 1/4 round anyway, but that would be a funny situation. There are hand held shear cutters for that, actually.
That's kind of a silly situation, but keep in mind the 420 rail is actually 32" long and the saw is 12 lbs or so. You can handle it with one hand but it's not likely to be simple to learn to do juggling with it. Such situations are not likely to be common. I bought the HK so I don't have to have a sliding miter saw on site. I have a Metabo Secanta, which is portable slide table saw, so the HK adds pick-up and cut speed out of the truck but I have the Secanta in there too. Between them they don't replace a sliding 12" miter saw for running mitered moulding all day, but for crosscuts the HK is light and easy to get set up.